Blast furnace

ABSTRACT

A blast furnace of the shaft furnace type for continuously smelting treated iron ores into liquid pig iron includes a furnace wall of refractory materials. The furnace wall is surrounded by a metal jacket particularly in the lower portion of the blast furnace, the bosh and the hearth arranged underneath the bosh. The blast furnace further includes water-cooled cooling elements, for example, plate-type cooling elements arranged between the refractory furnace wall and the metal jacket. At least those of the water-cooled cooling elements arranged in the hearth area of the blast furnace and between the hearth furnace wall and the metal jacket surrounding the hearth furnace wall are made of a material of high thermal conductivity, such as copper, wherein the thermal conductivity is at least five times the thermal conductivity of cast iron.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a blast furnace of the shaftfurnace type for continuously smelting treated iron ores into liquid pigiron. The blast furnace includes a furnace wall of refractory materials.The furnace wall is surrounded by a metal jacket particularly in thelower portion of the blast furnace, the bosh and the hearth arrangedunderneath the bosh. The blast furnace further includes water-cooledcooling elements, for example, plate-type cooling elements arrangedbetween the refractory furnace wall and the metal jacket.

[0003] 2. Description of the Related Art

[0004] When smelting treated iron ores in the blast furnace by reductionand partial combustion of the reducing agents, high temperatures whichmay be up to 1,600° C. and more are reached in the lower portion of theblast furnace. The pig iron obtained by reduction at these hightemperatures is present in liquid form and collects at the bottom in thelowermost portion of the blast furnace, i.e., the hearth, with layers ofmolten slag above the pig iron.

[0005] The pig iron collecting in the hearth and the liquid slag arewithdrawn or tapped from time to time through appropriate openings andare supplied to their further use.

[0006] In order to keep the blast furnace mechanically stable at thesehigh temperatures and the reducing conditions prevailing in the blastfurnace, the furnace wall is made of a refractory material which issuitable for these conditions, wherein the furnace wall is at least inthe lower portion thereof surrounded by a metal jacket or casing.

[0007] While alkali vapors and carbon monoxide attack and destroy therefractory materials in the upper zones, wherein carbon is depositedwithin the refractory materials, an infiltration of liquid metals, metaloxides and slags, which also leads to a disruption of the refractorymaterials, takes place in the lower zones of the blast furnace.

[0008] In order to minimize and avoid as much as possible theseundesirable infiltrations, a principal requirement of these refractorymaterials, in addition to a high refractoriness under load, is a highapparent density with an appropriately low open porosity. However, asufficient durability of the refractory materials can only be achievedif they are additionally cooled from outside, usually by a water coolingsystem.

[0009] For the area of the blast furnace hearth or the lower portion ofthe blast furnace, in which the liquid pig iron collects and the liquidslag collects above the pig iron, basically different cooling systemsare known in the art, namely, those that are effective outside of theslag furnace casing and those that are effective within the blastfurnace casing, as extensively described in “Hutte”, Taschenbuch furEisenhüttenleute, Verlag Stahleisen mbH, Düsseldorf 1961, pages 530 and531.

[0010] The external cooling is realized either by an open sprinkling ofthe hearth casing with water or by guiding the cooling water by means ofcooling cassettes welded parallel onto the metal casing.

[0011] Used for the internal cooling are water-cooled, plate-typecooling units of cast iron which are arranged between the refractoryfurnace wall and the blast furnace casing and extend parallel to thecasing. The cooling water is conducted in steel pipes which are castinto the body of the plate-cooling unit. The pipes extend to the outsidethrough appropriate openings in the blast furnace casing where they areconnected to a cooling supply line and a cooling water discharge line.

[0012] In spite of these known intensive cooling devices, it frequentlyoccurs after a failure of the refractory hearth wall under the influenceof the liquid phases which act from the inside on the refractorymaterials, that the blast furnace casing melts through in the area ofthe hearth wall, which causes an uncontrolled discharge of liquidphases, i.e., slags, pig iron, solid components, i.e., coke, charge,and, until the blast furnace is without pressure, even gases.

[0013] In this connection, even the known hearth wall cooling systemsfail when a direct contact occurs with the liquid pig iron because, dueto their low thermal conductivity, they are not capable of removinggreat quantities of heat from the liquid pig iron so rapidly that thepig iron solidifies before the material of the cooling elements or thehearth casing melts.

[0014] Both cooling systems described above are not capable ofcontaining pig iron within the hearth if the refractory brick lining ofthe casing fails. A break-out is unavoidable in such a case.

[0015] Break-outs cause disruption in the entire furnace area because ofthe direct influence of emerging materials, by irradiation heat and byoxyhydrogen gas explosions which may occur when water from defectivecooling elements comes into contact with pig iron. As a consequence ofsuch damage, the blast furnace is frequently not usable for a longerperiod of time which may be days to weeks. A characterizing feature ofmany break-outs is the fact that they occur suddenly and without anywarning indications. The cause of the break-out can in most cases not bereconstructed or traced because of the destruction in the area of thebreak-out point.

[0016] Therefore, in addition to the costs of the actual repair,especially the losses due to production interruption must be mentioned.Since the production is today concentrated in a few blast furnaces ofthe highest capacity and, thus, due to lacking replacement capacities,these losses have become increasingly important.

SUMMARY OF THE INVENTION

[0017] Therefore, it is the primary object of the present invention toimprove cooling of the blast furnace hearth in such a way that theliquid phases can no longer melt through the blast furnace casing whenthe refractory brick lining of the hearth fails for any reason.

[0018] In accordance with the present invention, the water-cooledcooling elements arranged in the hearth area of the blast furnacebetween the hearth furnace wall and the metal jacket surrounding thehearth furnace wall, i.e., the hearth casing, are made of a material ofhigh thermal conductivity, wherein the thermal conductivity is at leastfive times the thermal conductivity of cast iron; for example, thematerial of the cooling elements is copper.

[0019] The measure according to the present invention makes it possiblethat in the case of a break-out through the refractory brick lining, theliquid pig iron solidifies into a solid layer on the plate-type coolingelements or already on the other side of the refractory hearth wall.Consequently, the cooling system has a self-protective mechanism becausethe solidified layer protects against another attack by liquid pig ironor liquid slag. In addition, time is gained and it is made possible tostop operation of the blast furnace in a planned manner and to preparefor the necessary repair work.

[0020] The measures according to the present invention are limited tothe system of internal cooling because the thermal resistance of thehearth casing proper is not significantly reduced if the externalcooling elements are made of a material of high thermal conductivity.

[0021] If, in accordance with the present invention, copper is used asthe material of high thermal conductivity, wherein the thermalconductivity of copper at 20° C. with lambda=370 W/m.K is almost tentimes greater than that of the normally used iron in the form of castiron, the possible danger of a break-out is significantly reduced whenan appropriately large quantity of cooling medium in the form of wateris used.

[0022] In accordance with another advantageous feature of the presentinvention, the material of high thermal conductivity can also be used inthe form of appropriately constructed cooling elements for an intensivecooling of the hearth bottom. In this manner, it is also possible toprevent damage to the refractory lining at the hearth bottom which mightresult in indentations in the bottom (furnace sow) which frequently mayreach a depth of several meters during longer periods of operation ofthe blast furnace.

[0023] The intensive and extremely rapidly acting cooling according tothe present invention not only successfully prevents the occurrence ofbreak-outs, but the now substantially more intensive cooling as comparedto conventional cooling systems makes it possible to use uniform wallthicknesses of the usually prefabricated refractory material in thehearth. Since the refractory material is cooled more intensively thanwas the case in the past and, thus, the thermally caused wear as aresult of the contact with the liquid phases progresses more slowly andstops more slowly than was the case previously, it is now possible toconstruct the refractory material at these locations more uniformly,i.e., they can be thinner. This also makes it possible to construct thehearth casing cylindrically in the case of new constructions and thepreviously used conically widening shape toward the bottom for receivingadditional refractory material volume is no longer required. In additionto saving costs of the refractory materials by rendering the wallthicknesses uniform in the hearth area, also eliminated is the previousdisadvantage that the internal pressure of the furnace and the thermalexpansion of the refractory material in the previous conicalconfiguration produce significant forces perpendicularly of the furnacefoundation which had to be absorbed by appropriately dimensioned andexpensive anchoring systems.

[0024] The various features of novelty which characterize the inventionare pointed out with particularity in the claims annexed to and forminga part of the disclosure. For a better understanding of the invention,its operating advantages, specific objects attained by its use,reference should be had to the drawing and descriptive matter in whichthere are illustrated and described preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWING

[0025] In the drawing:

[0026]FIG. 1 is a vertical sectional view of a blast furnace, and

[0027]FIG. 2 is a sectional view, on a larger scale, of a detail of theblast furnace of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]FIG. 1 of the drawing shows in a vertical sectional view anembodiment of a blast furnace 1 substantially of conventionalconstruction in which treated iron ores are smelted in accordance withthe counter-current flow principle. The blast furnace 1 is in the knownmanner essentially divided into four different portions, i.e., thefurnace top 2, the shaft 3, the bosh 4 and the hearth 5.

[0029] The charging materials, including the ores, additives and coke asthe reducing agent, are added to the blast furnace 1 at its upperportion, i.e., the furnace top or throat 2. Flowing against the chargingmaterials which move downwardly slowly during the travel through thefurnace is the air blast which is heated outside of the blast furnace,not shown in the drawing, and is blown into the lower portion of theblast furnace 1 through a ring line 11 and blast tuyeres 6. The chargingmaterials are heated by this air blast and combustion reactions and thereduction of the iron ore take place. These reactions take place in themiddle portion of the blast furnace 1, i.e., the shaft 3 and in the bosh4 therebelow, so that molten pig iron and molten slag are formed whichcollect in the hearth 5, wherein the liquid pig iron settles because ofits higher density underneath the slag. The liquid pig iron isdischarged or tapped through outlet openings which are located on thelevel of arrow 10. Outlet openings for the molten slag are providedabove the outlet openings for the pig iron, however, these outletopenings are not shown in FIG. 1.

[0030] The hearth 5 is surrounded by a suitable brick lining ofrefractory materials 7, 7′ which, when contacted by molten iron andmolten slag, is essentially resistant and is not destroyed. Therefractory brick lining 7 of the hearth 5 extends upwardly to the levelof arrow 9.

[0031] According to the present invention, arranged between thisrefractory brick lining 7 and the surrounding metal jacket 8, i.e., thehearth casing, are cooling elements 13, for example, plate-type coolingelements, which, according to the present invention, are made of amaterial of high thermal conductivity. In accordance with the presentinvention, these cooling elements are also arranged in the hearth bottom12.

[0032] The intensive cooling action taking place as a result of themeasures of the present invention make it possible, particularly in thecase of new constructions of blast furnaces, to construct the obliquelyoutwardly extending portion 7′ of the refractory brick material 7 moreuniformly and cylindrically, so that refractory material is saved andthe now also cylindrical hearth casing can be installed without theotherwise required cost-intensive anchoring systems.

[0033]FIG. 2 of the drawing shows the feature according to the presentinvention in a partial sectional view on a larger scale. Specifically,FIG. 2 shows in a simplified illustration the hearth 5, the bosh 4 andthe lower portion of the shaft 3 of the blast furnace 1. The hearth 5and the bosh 4 are constructed of a refractory material, i.e., the bricklining 7, 7′ which is surrounded by a metal jacket 8, i.e., the casing.In the illustrated embodiment, the refractory brick lining 7 extendsupwardly to the upper end of the bosh 4.

[0034] Arranged between the metal jacket 8 and the refractory bricklining 7, 7′ are cooling elements 13 which, according to the presentinvention, are made of a material of high thermal conductivity, forexample, copper. As shown in FIG. 2, these cooling elements 13 extendfrom the hearth bottom 12 past the blast tuyeres 6 up to the level ofarrow 9. The cooling elements 13 are connected to a pipe system 14arranged outside of the metal jacket 8. The pipe system 14 ensures thatthe cooling elements 13 are supplied with a sufficiently high quantityof cooling water.

[0035] Because of their relative size, the cooling elements 13 are mayschematically illustrated in FIGS. 1 and 2 of the drawing. Accordingly,the specific configuration of the cooling elements 13 is not shown inthe drawing. However, this is not required because conventional andproven cooling elements, such as plate-type cooling elements, can beused, as long as they are made of a material of high thermalconductivity, for example, copper, as provided by the present invention.

[0036] While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

We claim:
 1. A blast furnace of shaft furnace construction for thecontinuous smelting of treated iron ores into liquid pig iron, the blastfurnace comprising a furnace wall of refractory materials, a bosh and ahearth underneath the bosh and a metal jacket surrounding at least alower portion of the blast furnace, the bosh and the hearth, furthercomprising water-cooled cooling elements arranged between the refractoryfurnace wall and the metal jacket, wherein the water-cooled coolingelements arranged in an area of the hearth of the blast furnace are of amaterial having a high thermal conductivity, and wherein the thermalconductivity is at least five times that of cast iron.
 2. The blastfurnace according to claim 1, wherein the cooling elements areplate-type cooling elements.
 3. The blast furnace according to claim 1,wherein the material of high thermal conductivity is copper.
 4. Theblast furnace according to claim 1, further comprising additionalwater-cooled cooling elements of a material of high thermal conductivityarranged in a hearth bottom.
 5. The blast furnace according to claim 4,wherein the additional cooling elements are of copper.
 6. The blastfurnace according to claim 1, wherein the refractory furnace wall has auniform wall thickness in the area of the hearth, and wherein the metaljacket surrounding the furnace wall in the area of the hearth is ofcylindrical construction.